1. Technical Field
The embodiments herein generally relate to wireless communication systems, and, more particularly, to mobile television (TV) technologies.
2. Description of the Related Art
As shown in FIG. 1, in many wireless communication channels 100, such as Terrestrial-Digital Multimedia Broadcasting (T-DMB), on the transmitter side, convolutional encoding (101) is applied on the transmitted data to provide robustness of transmission against transmission errors. To provide further immunity against burst errors, time interleaving (102) is used to spread the encoded bits over a wide time span. The interleaved bits are then mapped (103) to quadrature amplitude modulation (QAM) symbols that are then transmitted on the channel 100. At the receiver, the received QAM symbols are demapped (104) to soft decisions. Each soft decision is usually represented in hardware by N bits. Deinterleaving (105) is performed on the soft decisions which are then decoded to obtain the original transmitted data bits using a Viterbi decoder 106. The use of interleaving (102) makes the receiver more immune to burst errors because the burst errors on the physical channel will be spread by the deinterleaver 105 and reach the Viterbi decoder 106 as spread errors.
In T-DMB, for example, time interleaving is applied to each of the subchannels of the Main Service Channel (MSC). This time interleaving is used to spread the encoded bits over a wide time span. The receiver requires memory for the deinterleaver 105 to store the delayed bits in order to reverse the interleaving order. The required memory at the receiver is directly proportional to the number of bits (N) that the demapper 104 uses to represent each soft decision. For T-DMB, the receiver memory size is a significant portion of the entire receiver size (approximately 20 to 30%). Clearly, reducing N, and thus reducing the receiver cost, is highly desired. However, the performance of the receiver deteriorates with decreasing N, especially in fast fading channel conditions. Accordingly, there remains a need for a technique of reducing receiver memory requirements in wireless communications systems.